docs(LamNI): document smear aid architecture and camera/GUI interfaces

Add docs/developer/lamni_smear_architecture.md covering the three-tier
device/ipython-client/GUI architecture this feature exercises: the
camera's two PreviewSignal channels (image vs smear_preview) and why
composite pushes needed their own channel, XRayEye.set_live_view_signal
and exactly when the caller must switch it back, the sweep algorithm
(non-blocking mv() + ScanReport.status polling + max-projection), and
the bw-generate-cli regeneration step required whenever a plugin
widget's USER_ACCESS changes (the cause of this session's confusing
AttributeError even after a full client/GUI restart).

Also expand the user-facing description in lamni.md with a note on the
live-updating composite display and a cross-reference to the new
developer page.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docs/developer/developer.md

@@ -9,6 +9,7 @@ hidden: true
 ---
 
 editing_docs
+lamni_smear_architecture
 
 ```
 
@@ -30,4 +31,15 @@ editing_docs
 Conventions for writing these MyST/Sphinx docs and how changes go live on Read the Docs.
 ```
 
+```{grid-item-card}
+:link: developer.lamni_smear_architecture
+:link-type: ref
+:text-align: center
+:class-item: index-card
+
+## LamNI smear aid architecture
+
+Device/ipython-client/GUI widget interfaces for the smear rotation-center calibration aid, and the `bw-generate-cli` regeneration pitfall.
+```
+
 ````